1. Field of the Invention
The present invention relates to a remote control system for remotely controlling movement of a mobile body along a guideway.
2. Description of the Related Art
Use of various automated operating machines for laborsaving is prominent in recent years in manufacturing facilities of semiconductor circuits, which require ultraprecision machining, and in factories of various machine parts. Transfer boots, dollies, and other mobile bodies that automatically move to a predetermined destination are used to convey materials for operating machines, processed products, and various machining tools.
Most of these mobile bodies have an antenna (i.e., a coupling device) for noncontact wireless communications through electromagnetic induction coupling between the mobile body and a guideway arranged in a factory or warehouse.
The antenna of the mobile body allows bidirectional communications between the mobile body and a fixed control apparatus. More specifically, various control signals for controlling the mobile body are output by the fixed control apparatus, transmitted via the guideway, and received by the antenna of the mobile body. Also, various radio-frequency waves that have been modulated by a signal of the mobile body are output on the antenna and received by the fixed control apparatus connected to the guideway.
Japanese Patent Application Publication S61-224735 discloses a conventional communications system. The conventional communications system includes: (a) a mobile body having a loop antenna, and (b) a guideway. More specifically, a balanced cable, which serves as the guideway, is arranged on the floor, and the mobile body is slid along the guideway through electromagnetic coupling or electric field coupling established by its loop antenna for communications between the mobile body and a fixed apparatus connected to the guideway.
Japanese Patent Application Publication 2005-045327 discloses a coupling device for communications between a mobile body and a ground-side guideway, where communications are made mainly through inductive magnetic field coupling.
FIG. 12 of the latter document schematically illustrates a conventional remote control system for controlling the mobile body using the coupling device. The guideway 1 may be arranged on a surface of a floor or hung from a ceiling. The guideway 1 is a balanced feeder line with two parallel wires 1a, 1b held and supported by a dielectric material 1c. 
Also, the coupling device 2, which serves both as a receiving device and as a transmission antenna, is disposed at a predetermined portion of the transfer dolly 3. The coupling device 2 has one electrostatically shielded loop antenna in a shape of a loop for receiving a radio-frequency wave that goes out of the feeder line 1 and transmitting information from the transfer dolly 3.
In general, the strength of an electromagnetic field given rise to by a wave source can be divided into components that change depending upon a distance R from the wave source to a radio equipment. The components can be schematically classified into a quasi-electrostatic field component (1/R3), that is inversely proportional to the cube of the distance R, an induced electric field component (1/R2), that is inversely proportional to the square of the distance R, and a radiation electromagnetic field component (1/R), that is inversely proportional to the distance R.
As shown in FIG. 13, although the 1/R3 component and the 1/R2 component attenuate rapidly as the distance R becomes larger, the 1/R component can travel a relatively long distance.
The conventional mobile body remote control system shown in FIG. 12 employs inductive magnetic field coupling for communications between the balanced feeder line T and the coupling device 2 that are proximate to each other.